docs: def diameter(self):
          '''Compute the diameter (maximum leaf pairwise distance) of this ``Tree``
  
          Returns:
              ``float``: The diameter of this Tree
          '''
          d = dict(); best = float('-inf')
          for node in self.traverse_postorder():
              if node.is_leaf():
                  d[node] = 0
              else:
                  dists = sorted(d[c]+c.edge_length for c in node.children)
                  d[node] = dists[-1]; max_pair = dists[-1]+dists[-2]
                  if max_pair > best:
                      best = max_pair
          return best